No. 11 5 5 4 6 151 6 4 5 5 215 2 8 2 8 213 2 8 5 5 225 4 6 2 8 227 4 6 6 4 235 6 4 4 6 415 2 8 4 6 425 5 5 8 2 229 2 8 5 5 Averages 3.8 6.2 4.5 5.5 That the dancers should prefer to enter the dark rather than the light box is not surprising in view of the fact that the nests in which they were kept were ordinarily rather dark. But whatever the basis of the preference, it is clear that it must be taken account of in the visual discrimination experiments, for an individual which strongly preferred black might choose correctly, to all appearances, in its first black-white series. Such a result would demonstrate preference, and therefore one kind of discrimination, but not the formation of a habit of choice by discrimination. The preference for black is less marked in the second series of tests because the mouse as it becomes more accustomed to the experiment box tends more and more to be influenced by other conditions than those of brightness. The record sheets for both series almost invariably indicate a strong tendency to continue to go to the left or the right entrance according to the way by which the animal escaped the first time. This cannot properly be described as visual choice, for the mouse apparently followed the previous course without regard to the conditions of illumination. We have here an expression of the tendency to the repetition of an act. It is only after an animal acquires considerable familiarity with a situation that it begins to vary its behavior in accordance with relatively unimportant factors in the situation. It is this fact, illustrations of which may be seen in human life, as well as throughout the realm of animal behavior, that renders it imperative that an animal be thoroughly acquainted with the apparatus for experimentation and with the experimenter before regular experiments are begun. Any animal will do things under most experimental conditions, but to discover the nature and scope of its ability it is necessary to make it thoroughly at home in the experimental situation. As the dancer began to feel at home in the visual discrimination apparatus it began to exercise its discriminating ability, the first form of which was choice according to position.